Cationic modified epoxy resins used in cathodic electrodeposition paint formulations are produced by reacting a starting epoxy resin with an amine to open the epoxy group with the amine in order to render the resin hydrophilic and cationically chargeable. The resulting amine-modified resin and a crosslinker such as blocked polyisocyanates are then emulsified in an aqueous medium containing a neutralizing agent for use in the electrodeposition coating process.
The amine-modified epoxy resins of this type per se are not easily emulsifiable in an aqueous medium and thus require a surfactant. It has been discovered that even when emulsified with the aid of conventional surfactants, the resin can only be emulsified into particles of relatively large particle sizes which tend to settle upon standing.